Michio Araki

Breakdown of Passive Film on Iron

Abstract The breakdown of passive films potentiostatically formed on iron in borate and phosphate solutions of pH 8.42 and 11.50 is investigated in 0.5 kmol/m3 NaCl solution at a constant potential of −0.195 V(SHE) higher than a critical pitting potential of −0.295 V in the same solution. The investigation revealed that the logarithmic plots for pitting current (ip) or amount of electric charge (Qp) vs time curves were composed of two straight lines with different slopes after a short period in which ip scarcely flows. The time, τ, required for the transition from the first to the second line was found to be a linear function of passivation potential irrespective of anion species and solution pH in which a passive film was formed. However, the slope of their linear relation depended on anion species and solution pH. It is believed that the first straight line corresponds to pit nucleation and the second one to pit growth. The dependence of τ on log (Cl−) gives the critical chloride ion concentration of 0....

FRACTURE TOUGHNESS AND FATIGUE CRACK GROWTH OF AISI 4340 STEEL IN HIGH PRESSURE HYDROGEN AT ROOM TEMPERATURE

The fracture toughness and the fatigue crack growth properties of the annealed, quenched and quenched-tempered AISI 4340 steel were investigated in high pressure hydrogen up to 9.9 MPa at room temperature. The effect of gaseous inhibitors added to hydrogen atmosphere on the fatigue crack growth of the steel to prevent hydrogen assisted fatigue crack growth was also examined. The following conclusions were drawn from the results: (1) The fracture toughness of the quenched steel both in argon and in hydrogen were almost constant at the stress intensity rate range tested. In all conditions of heat treatment the fracture toughness in hydrogen was smaller than that in argon and decreased with increasing hydrogen pressure. (2) The fatigue crack growth of the steel in hydrogen was higher than that in argon in all conditions of heat treatment. The order of hydrogen susceptibility of the heat treated steel was as follows; the annealed steel < the quenched one < the quenched-tempered one. (3) Carbon monoxide, oxygen or sulfur dioxide has much effect on preventing hydrogen assisted fatigue crack growth, but carbon dioxide, methane, water vapor or methyl mercaptan had little effect. On the other hand, hydrogen sulfide accelerated the fatigue crack growth.